Field of the Invention
The invention lies in the sheet processing field. More specifically, the invention relates to a delivery for a sheet-processing machine, particularly for a sheet-fed offset printing machine.
Reference is had to U.S. Pat. No. 4,479,645 (see German published patent application DE 31 13 750 A1), which provides an example of a sheet delivery.
Deliveries of the type described here are located at the end of a sheet processing apparatus, such as at a sheet-fed printing machine. They comprise revolving guide chains with gripper bridges which grasp the individual sheets and convey them to a stacking shaft. A delivery stack is formed therein. Various requirements related to careful handling of the paper and the printed image must be satisfied in the delivery process. Specifically, care must be taken that neither the printed image nor the sheets are damaged, which could be disadvantageous in post-processing.
In order to guarantee a gentle and controlled delivery, braking devices are provided, which are known as brake modules. These may be formed, for example, of a plurality of suction disks or suction tapes which are disposed on a horizontal shaft that extends transverse to the direction of sheet transport. By means of the braking modules, a suction force can be brought to bear on the sheets in order to decelerate them and prevent the sheets from hitting the appertaining stops of the stacking shaft with force.
The brake modules must be arranged such that, seen perpendicular to the direction of sheet transport, they only make contact with unprinted regions of a sheet which has been printed on both sides (perfecting), so that the printed image is not impaired.
Since the uninked regions extend in different locations of the sheet from one copy to the next, as seen perpendicular to the direction of sheet transport, the brake modules must be variably positionable in the perpendicular direction, accordingly.
Depending on the printed image, a variably large number of brake modules can be used. For some printed images, only three brake modules are used. In such a case, the sheet may slacken between two adjacent brake modules, causing the sheet with its printed image to rub against components of the machine, which leads to smearing of the printed image. This, of course, is unacceptable.
Such cases require that the sheet be supported in the regions between the brake modules. Guide straps may be considered as support elements. These also may be used only in unprinted regions, though these regions need not be as wide as with brake modules. Due to the givens in the delivery, the sheet cannot always be guided precisely orthogonally during the entire depositing process, and therefore the guide straps may also come in contact with printed regions and cause the ink to smear.
What are known as starwheels have also been used as support elements. These can be used in printed regions as well; however, they cause a certain marking of the printed image.
It has also become known to bridge the interspaces between the brake modules using sheet guide plates. The width of the sheet guide plates perpendicular to the direction of sheet transport is dimensioned such that they close off the interspace between two adjacent brake modules. It is thus possible to build an air cushion between the individual sheet guide plate and the bottom of the sheet, as a consequence of which the sheet can be transported without smearing. However, it is difficult and time-consuming to work with such guide plates. The guide plates can be attached only after the individual brake modules have been preset to the current subject. It is also necessary to tailor the guide plates to the respective distance between the brake modules. This requires a number of plates of varying widths from one job to the next. Adjusting the position of the brake modules during the press run is out of the question.
U.S. Pat. No. 5,358,236 (German published patent application DE 42 11 922 A1) describes a table cover device for a sheet-fed printing machine. The object of that type of device is to create a feed table cover in the region of the side lays for secure sheet guidance.
All the prior art guide mechanisms preclude a completely remote operation of the sheet brake. This is so because manual set-up procedures are always required in order to adjust the brake module to the current subject.
It is accordingly an object of the invention to provide a delivery for a sheet processing machine, particularly for a sheet-fed printing machine, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allows the braking function to be executed perfectly. Thus, the actual braking function should be fulfilled as desired. Sagging of the sheet and thus smearing are prevented. Marking by support elements is also avoided. Lastly, the sheet brake is intended to be remote-controllable, so that manual set-up procedures are no longer needed for adjustment purposes. Remote operation and/or automation should be possible.
With the foregoing and other objects in view there is provided, in accordance with the invention, a delivery for a sheet processing machine wherein sheets are delivered in a sheet transport direction, comprising:
a plurality of braking devices displaceably disposed transverse to the sheet transport direction and forming interspaces therebetween with a variable spacing; and
sheet guiding elements respectively covering the interspaces between adjacent braking mechanisms, the sheet guiding elements including a tape of flexible material having a length, transverse to the sheet transport direction, as seen from above, adjustable to the spacing between the adjacent braking devices.
In accordance with an added feature of the invention, the sheet guiding elements comprise:
a tape between each two adjacent braking devices and having a first end and a second end;
a dispensing roller with a longitudinal axis parallel to the sheet transport direction allocated to one of two adjacent braking devices;
the first end of the tape surrounds the dispensing roller and the second end of the tape is fastened to the respectively other braking device; and
a winding drive allocated to the dispensing roller.
In accordance with an additional feature of the invention, the winding drive is a spring disposed to bias the dispensing roller to continuously keep the tape taut. In the alternative, or additionally, the winding drive is a motorized winding drive or a pneumatic winding drive.
In accordance with an alternative feature of the invention, the sheet guiding elements comprise:
a single tape for all the braking devices;
the single tape having two ends respectively fastened to lateral frames of the delivery;
the tape surrounding the individual the braking devices and wrapping around the braking device underneath.
In accordance with another feature of the invention, guide rolls are provided for guiding the tape.
In accordance with again a further feature of the invention, a respective tape is provided between each two adjacent braking devices; each end of the tape is fastened to one of the braking devices; and a dancer roller, which carries a memory loop of the tape, is disposed to compensate a length change of the tape given changes in the spacing between the brake devices.
As noted above, the delivery is particularly suitable for a sheet-fed printing machine. In that case, there is provided, in accordance with the invention,
a data memory for storing data related to an image to be processed in the printing machine;
a computer for generating control signals correlated with unprinted corridors of the image;
and the braking devices are configured to be adjustable by actuating drives controlled by the control signals generated by the computer, into positions correlated with the unprinted corridors.
In accordance with again an added feature of the invention, an image reader configured to set and read into the data memory the data correlated with the image. The image reader may be a CCD camera. Where the printing machine transfers images via printing forms, the image reader may advantageously be a plate reader.
In accordance with again another feature of the invention, a plurality of dispensing rollers form sections of a flat structure.
In accordance with a concomitant feature of the invention, the tape is a flexible one-piece flat structure deflected about a plurality of guides defining segments of the flat structure.
The inventors have taken a new path. They have selected a tape of flexible material as the sheet support element. They have taken precautions to make the length of the tape, as seen perpendicular to the direction of sheet transport and from above, adjustable to the distance between the mutually spaced brake elements. Between the inventive tape-shaped sheet guide element and the bottom of the sheet, an air cushion can be formed, which supports the sheet and prevents it from sagging and thereby prevents smearing. The air cushion is continuously maintained, notwithstanding the adjustability of the brake modules.
Different variants are conceivable for realizing the inventive idea.
According to the first variant, as outlined above, a tape can be allocated to respective adjacent brake modules. One of the ends of the tape is fastened to one of the two brake modules, while the other end of the tape is wound onto a spool (roller) which is disposed at the other brake module, with its longitudinal axis extending in the direction of sheet transport. In this exemplifying embodiment, if two adjacent brake modules are repositioned relative to each other, i.e. if the spacing between them is expanded or reduced, the tape is wound from or onto the roller. The roller is provided with a winding drive. This can consist of a spring, as in a window shade mechanism. In this case, the tape automatically remains taut, regardless of the spacing between the two brake modules, so that the tape extends in a plane and does not develop any creases. This has a positive effect on the formation of the air cushion which forms between the tape and the bottom of the sheet. No further influencing of the functioning of the tape is required.
Alternatively, a motorized or pneumatic drive can be provided, which is controlled in dependence upon the positioning of the appertaining brake module.
According to a second variant, only a single tape is provided. The two ends of the tape are fastened to the lateral parts of the frame of the press. The tape wraps around the individual brake modules such that it surrounds the appertaining module underneath.
To guide the tape, guide rolls can be provided at all guide points, except when a roller is used. These naturally extend with their longitudinal axes in the direction of sheet transport as well.
The following solution is proposed as a third variant: A tape is provided between two adjacent brake modules, with one of its ends fastened to one module, and the other end fastened to the other module. A memory loop with dancer rolls is provided to compensate the length of the tape when the spacing between the modules changes.
It is understood that the tape must be situated at a height that is substantially within the region of the working plane of the brake modules. The gap which necessarily emerges (in a plan view) between the brake module and the tape should be optimally small. To this end, if a roller is used it is best to lead the tape by means of a guide roll to the relevant brake module which bears the former roller.
Any kind of rollable material may be used as the material for the tape, for instance a foil, a (dense) fabric, or a sheet which is extremely thin.
The inventive principle can be applied particularly effectively given straight printing and perfecting operations. In this method, the sheet is turned as it runs through the machine in order to enable printing on the other side.
The invention is not limited to using a specific brake module design. The individual brake module can substantially comprise a suction disk whose axis extends in a horizontal plane and transverse to the direction of sheet transport. But it is also possible to provide two rollers or drums, also with their respective axes arranged in a horizontal plane and transverse to the direction of sheet transport.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a delivery for a sheet processing machine, particularly for a sheet-fed printing machine, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.